The present invention relates to an exposure apparatus, an apparatus for manufacturing devices, and a method of manufacturing exposure apparatuses, which are employed in transferring a mask pattern onto a substrate in a lithography process for producing microdevices such as, for example, semiconductor elements, liquid crystal display elements, image pickup elements, or thin film magnetic heads or the like, and are preferably employed when exposure light in the ultraviolet band having a wavelength of approximately 400 nm or less, and particularly when exposure light of the vacuum ultraviolet (VUV) band having a wavelength of 200 nm or less, is employed.
In exposure apparatuses such as steppers or the like which are employed, for example, in the manufacture of semiconductor devices, in order to provide an increase in the degree of integration or minuteness of the semiconductor devices, an increase in resolution is particularly necessary. This resolution is essentially proportional to the wavelength of the exposure light, so that conventionally the wavelengths of the exposure light were progressively shortened. That is to say, the exposure light employed changed from the g line in the visible band of mercury lamps (wavelength 436 nm) to the i line in the ultraviolet band (wavelength 365 mn), and recently, KrF excimer laser light (wavelength 248 nm) has come to be employed. Additionally, presently, ArF excimer laser light (wavelength 193 nm), F2 laser light (wavelength 157 nm) and Ar2 laser light (wavelength 126 nm) are being considered for use. Furthermore, in conventional X-ray lithography research, the use of light having wavelengths of 13 nm, 11 nm, or 7 nm, which are in the so-called extreme ultraviolet (EUV or XUV) band and are close to X-rays, and the use of X-rays having a wavelength of approximately 1 nm, has been considered.
However, when wavelength bands of less than approximately that of ArF excimer lasers, that is to say, the vacuum ultraviolet band (VUV) of approximately 200 nm or less, are employed, absorption occurs as a result of the oxygen in the air, and ozone is produced, and transmittivity declines. In exposure apparatuses which employ ArF excimer laser light, for example, the majority of the gas in the optical path of the exposure light is replaced by nitrogen, so that the so-called nitrogen purge is conducted. Furthermore, at wavelength bands of less than approximately that of the F2 laser, absorption occurs even with nitrogen. In this case, if the region of nitrogen passage is an extremely narrow region, the amount of absorption is slight, and no obstacle is presented to exposure; however, with a long optical path, the amount of light is reduced, and proper amounts of exposure can not be obtained. When light in a wavelength band shorter than the wavelength of the ArF excimer laser (less than approximately 190 nm) and particularly when light in the wavelength band of less than approximately the wavelength of the F2 laser, is employed, then it is necessary either to replace the majority of gas of the optical path of the light with another gas which allows transmission of light (an inert gas other than nitrogen), or to provide a vacuum.
On the other hand, when the exposure light passes an illumination optical system or optical elements, such as lenses and mirrors, within a projection optical system, then there is absorption of the beat energy by these optical elements as well. When the optical elements experience thermal expansion as a result of the heat energy absorbed in this way, this leads to degradation in image formation characteristic, such as changes in magnification, focal shift displacement, or the like. In order to prevent this degradation in image formation characteristic, conventionally, waste heat treatment was conducted, in which temperature controlling gases were caused to flow in predetermined spaces between lenses, and the side surfaces of lenses or the rear surfaces of mirror or the like were subjected to air cooling or liquid cooling, Recently, requirements have also increased with respect to stability of the image formation characteristic, so that an even higher level of treatment is required with respect to this waste heat treatment as well.
As described above, in exposure apparatuses, when exposure light in a wavelength band of approximately 190 nm or less is employed, it is desirable that the gas of the majority of the optical path be replaced with a gas having an absorption ratio smaller than nitrogen, or that this be made a vacuum. However, when the latter is done and the majority of the optical path is made into a vacuum, the manufacturing costs of the exposure apparatus increase, and the throughput of the exposure apparatus declines. Furthermore, in the exposure apparatus, it is desired that the heat energy of the exposure light be more efficiently exhausted.
In order to simultaneously address these problems, a gas may be supplied to the majority of the optical path of the exposure light, which gas is inert and has a high transmittivity and has good thermal conductivity (in other words, has a low atomic weight), and which is temperature controlled. Currently, the most highly functional gas for use as this type of inert gas having good thermal conductivity, and which is moreover stable, is helium (He). However, helium is present in the earth""s crust and in the atmosphere at an extremely low rate, and is high in cost, so that as the amount thereof used increases, the operational cost of the exposure apparatus rise greatly, and this is undesirable. Furthermore, because helium has a low atomic weight, it tends to leak from the gaps in the cover and the like which enclose the optical path of the exposure apparatus, and this presents a problem in that if helium is simply circulated within the cover, the amount of helium progressively decreases.
In view of these points, the present invention has as an object thereof to provide an exposure apparatus and a apparatus for manufacturing devices which, in the case in which a gas having a high transmittivity (inert) and having good thermal conductivity is supplied to at least a portion of an optical path of an exposure energy beam (exposure light), are capable of controlling the amount of this gas which is employed.
Furthermore, as described above, in the exposure apparatus, when exposure light having a wavelength of approximately 200 nm or less is employed, if the optical path of the exposure light is not made into a vacuum, it is necessary to replace the majority of the optical path of the exposure light with a gas having good transmittivity (such as nitrogen or the like). Furthermore, even where the wavelength is within a range of 250-200 nm, in order to obtain good transmittivity, it is desirable that the optical path of the exposure light be replaced with nitrogen or the like.
In connection with this, because the exposure apparatus is usually stored within a box shaped chamber having good airtightness and in order to conduct the positioning of reticles or wafers or the like in a highly precise manner in the exposure apparatus, a stage system, in which movement is conducted along a guide surface in the manner of an air bearing without contact, is provided. For this reason, when this type of stage system is employed, the compressed air sprayed along the guide surface leaks out into the chamber, and this air mixes with the gas having good transmittivity, such as nitrogen or the like, of the optical path of the exposure light, so that a problem is caused in that the transmittivity with respect to the exposure light progressively decreases. When the transmittivity decreases in this manner, the illumination intensity on the wafer decreases, so that in order to obtain the proper amount of exposure, it is necessary to lengthen the exposure period, and thus the throughput of the exposure process declines in an undesirable manner.
Furthermore, in the exposure apparatus, in addition to the stage system, equipment is provided for conducting positioning or vibration isolation or the like using air; there is also a danger that this air generated by this equipment will cause a decrease in the transmittivity of the exposure light.
In view of these points, the present invention has as an object thereof to provide an exposure apparatus which, in the case in which a predetermined gas having a high transmittivity is supplied to at least a portion of the optical path of an exposure energy beam (exposure light), is capable of guiding this exposure energy beam to the substrate which is the object of exposure such as a wafer or the like with a high use efficiency.
Furthermore, when conducting various exposure experiments by means of a projection exposure apparatus having a comparatively large field size using an excimer laser light source, the present inventors discovered a novel phenomenon, in which, by means of the application of illumination light in an ultraviolet wavelength band of, for example, 350 nm or less (a KrF exposure excimer laser having a wavelength of 248 nm, or a ArF excimer laser having a wavelength of 193 nm, or the like), the transmittivity or reflectivity of the optical elements or coating materials of the optical elements (for example, thin films such as reflection prevention films or the like) within the projection optical system varied dynamically. It has been made clear that this phenomenon of the dynamic flotation of transmittivity can be generated not merely with respect to the optical elements within the projection optical system, but also with respect to the optical elements or reticles (silica plates) themselves within the illumination optical system which illuminates the reticule or within the light transmission system which conveys the illumination light emitted from a light source positioned beneath the floor of the clean room to the illumination optical system within the exposure apparatus itself. In the present specification the term illumination optical system includes the light transmission system.
Such a phenomenon is thought to be produced when impurities contained within the gas (air, nitrogen gas, or the like) present in spaces within the projection optical path or the illumination optical path, molecules of organic matter generated by filler material or adhesives used to affix the optical elements to the barrel, or impurities (for example, water molecules, hydrocarbon molecules, or other substances which scatter the illumination light) generated from the inner wall of the barrel (the coated surface for preventing reflection or the like), are deposited on the surface of the optical elements, or enter into the illumination optical path (float). As a result a serious problem is caused in that the transmittivity or reflectivity of the projection optical system or illumination optical system can vary greatly within a comparatively short period of time.
It is an object of the present invention to provide a protection exposure apparatus which supports optical elements such as lenses or reflection mirrors or the like which comprise the projection optical system or illumination optical system without the use of adhesives or fillers.
The exposure apparatus in accordance with the present invention is, in an exposure apparatus having an illumination system (3, 11, 13, 14, 17-19) for applying an exposure energy beam to a mask forming a pattern for transfer, and a stage system (20-24) which positions a substrate to which the mask pattern is to be transferred, a gas supply apparatus (31, 43, 46) which supplies a gas having a high transmittivity with respect to the exposure energy beam and having good thermal conductivity to at least a portion of the optical path of the exposure energy beam, and a gas recovery apparatus (33-37, 41, 42) which recovers at least a portion of the gas dispersed after being supplied to the optical path of the exposure energy beam from the gas supply apparatus, are provided
In accordance with this present invention, because it is possible to recover and reuse (recycle) a portion of the gas supplied to the optical path, it is possible to control the amount of this gas employed. Accordingly, the operational costs decrease when the gas is high in cost.
In this case, an example of the gas is helium (He). Helium is safe and has a high transmittivity even when exposure light of the wavelength band of 150 nm or less is employed, and because the thermal conductivity thereof is high, being approximately 6 times that of nitrogen (N2), the cooling effect with respect to the optical element is high.
Furthermore, where the gas recovery apparatus recovers, for example, helium dispersed in the air, it is possible to separate the helium by processing the oxygen present in the mixed gas using an oxygen adsorbing material, and cooling the nitrogen, so that the remaining helium may be recovered. Alternatively, by cooling the mixed gas to the temperature of liquid air, and removing the liquid which is generated, it is easily possible to recover only the helium which remains in a gaseous state.
Furthermore, it is desirable that the gas recovery apparatus, be employed in common with a plurality of exposure apparatuses. By means of this, the equipment costs of the gas recovery apparatus are reduced.
Furthermore, it is desirable that the gas recovered by the gas recovery apparatus be recirculated to the optical path of the exposure energy beam via at least a portion (31, 43) of the gas supply apparatus.
Furthermore, the gas supply apparatus has, as one example, a concentration meter (44) for measuring the density of the gas supplied from the gas recovery system, a gas source (46) with the gas sealed therein in a gaseous state or in a liquid state, and control units (43, 45, 48) which supplement the gas supplied from the gas recovery apparatus with gas from the gas source (46) in accordance with the results of the measurement of the concentration meter. These control units supply gas from the gas source when the density of the gas measured by the concentration meter becomes lower than a predetermined allowable level. By means of this, the gas within the gas source is not used wastefully.
Furthermore, this gas supply apparatus is provided with, as an alternative example, a gas source (46) which conducts the liquid storage or high pressure storage of gas, a conversion apparatus which returns the liquid gas or high pressure gas within the gas source to a gaseous state, and an adjusting apparatus (43) which regulates the temperature and pressure of the gas from the gas source prior to its supply to the exposure apparatus. By means of this it is possible to store a large amount of the gas in a small space.
Furthermore, it is desirable that the gas recovery apparatus store the recovered gas in a liquefied or high pressure form. By means of this, it is possible to store a large amount of the gas in a small space.
Furthermore, the device manufacturing apparatus in accordance with the present invention is provided with a plurality of exposure apparatuses, including exposure apparatuses in accordance with the present invention, and using this plurality of exposure apparatuses, transfers a plurality of device patterns onto a substrate which is the object of exposure in an overlapping manner, producing microdevices. In this case, as well, the amount of gas employed can be controlled.
The exposure apparatus in accordance with the present invention is an exposure apparatus which illuminates a mask (R) with a predetermined energy beam, and transfers the pattern formed in this mask to a substrate (W), wherein a gas-controlled drive apparatus (123, 125A) which conducts predetermined operations (positioning, vibration isolation, and the like) using a first gas for control is provided, and a second gas having good transmittivity is supplied to at least a portion of the optical path of the exposure energy beam, and a gas of the same type as the second gas is employed as the first gas of the gas-controlled drive apparatus.
In accordance with this invention, the gas which is exhausted when the gas-controlled drive apparatus is driven is a gas of the same type as the second gas having good transmittivity with respect to the exposure energy beam, so that the concentration of the second gas supplied to the optical path of the exposure energy beam progressively decreases. Accordingly, the progressive decrease in the transmittivity with respect to the exposure energy beam is eliminated, and it is possible to guide the exposure energy beam to the substrate with a high efficiency of use.
In this case, an example of this gas-controlled drive apparatus is a stage apparatus (123) which makes contact with the guide surface in the form of a gas bearing system, a gas type cylinder apparatus, or a vibration isolation platform (125A) employing gas as a portion of the shock absorbing material. The exposure apparatus is normally contained within a box shaped chamber so that when a gas of a type other than the second gas is emitted from the gas-controlled drive apparatus the transmittivity of the exposure energy beam within the chamber progressively decreases; however, in accordance with the present invention a decrease in the transmittivity of the exposure energy beam within the chamber is prevented.
Furthermore, when the exposure energy beam is ultraviolet light having a wavelength of 250 nm or less, then it is desirable that the second gas be nitrogen (N2) or helium (He). In particular, since the transmittivity of nitrogen is good when the wavelength is from 250 to 200 nm, it is possible to employ low cost nitrogen. Furthermore, these gases are inert, so that fogging materials or the like will not be generated on the surface of the optical elements.
Furthermore, when the exposure energy beam is ultraviolet light having a wavelength of 200 nm or less, it is desirable that the second gas be helium. Helium has high transmittivity with respect to light of such short wavelengths, and additionally has particularly good thermal conductivity, so that its ability to cool the optical elements and the like is high. Furthermore, when, as an example of the wavelength of 200 nm or less, ArF excimer laser light having a wavelength of 193 nm is employed as the exposure energy beam, and a projection optical system comprising a cata-dioptric system is employed, the cata-dioptric system has fewer lenses than a refractive system, and the distance between lenses is greater, so that it is more susceptible to effects of fluctuations in atmospheric pressure. By purging the interior of the projection optical system comprising a cata-dioptric system with helium, which has a considerably smaller degree of change in the index of refraction in response to changes in air pressure, in comparison with nitrogen, it is possible to control the amount of fluctuation in the image forming characteristics at a low level.
Furthermore, when the exposure energy beam is an X-ray (for example, a wavelength within a range of approximately 10 nm-1 nm) then examples of the second gas are nitrogen or helium. Even when X-rays are employed, if the distances are short, the amount of attenuation can be kept at a low level.
The exposure apparatus (projection exposure apparatus) of the present invention is provided with an illumination optical system which applies illumination light from an illumination light source to a mask and which has a plurality of optical elements (9A, 9B, 11 . . . (109A, 109B, 111 . . . )) which are supported by support members, and with a projection optical system (PL) which projects the image of a pattern on a mask (original plate) onto an exposed substrate, which system is provided with a plurality of optical elements (L201, L202 . . . ) which are supported by support members. Additionally, all the optical elements described above arm supported on the support members using press-attachment mechanisms without employing adhesive, and thereby, the objects described above are obtained.
Furthermore, an example of this press-attachment mechanism is a flat spring (261), one end of which is affixed to the inner circumferencial part of the support member (251), and the other end of which presses against the outer circumferencial part of the optical element (L201, L202) at the other end.
Furthermore, another example of this press-attachment mechanism is one in which screwable attachment is conducted to a screw part attached to the inner circumferencial part of the support member (252), and a screw ring (263) is screwably advanced and presses the outer circumferencial part of the optical elements (L120-L205).
Furthermore, an exposure apparatus (projection exposure apparatus) in accordance with the present invention is provided with an illumination optical system (232) which has a plurality of optical elements (204, 205, 206 . . . ) containing fly eye lenses (11, 111) which bundle a plurality of rod lenses (L260) and which applies illumination light from an illumination light source (201) to a mask, as well as with a projection optical system which is provided with a plurality of optical elements (L201, L202, . . . ) which are supported by support members and which projects the image of a pattern on a mask (original plate) onto an exposure substrate. Then, by bundling a plurality of rod lenses (L260) using a support apparatus (280) without the use of an adhesive, the objects described above arm achieve
Furthermore, in a manufacturing method for exposure apparatuses in accordance with the present invention, a supply pipe for supplying a gas which reduces attenuation in the exposure energy beam is connected to a gas chamber which seals, in an essentially airtight manner, at least a portion of the optical path of the exposure energy beam, and a recovery pipe which recovers at least a portion of the gas supplied to the gas chamber is connected to at least one of the gas chamber and a housing in which the gas chamber is disposed. Then, the recovery pipe is connected to a removal apparatus which removes impurities from the recovered gas, and the removal apparatus and the supply pipe are connected. Furthermore, the optical elements which the exposure energy beam passes are assembled in the exposure apparatus by being fixed to support members without the use of adhesive. Furthermore, a gas control type drive apparatus which employs a gas having optical characteristics which are essentially the same as those of the gas which is disposed in the exposure apparatus, and a supply source for this gas, are connected.
In accordance with this invention, a portion of the gas supplied to the optical path may be recovered and reused (recycled) so that it is possible to control the amount of this gas which is employed, and it is thus possible to construct an exposure apparatus which makes possible a reduction of operational costs.
In this section disclosing the invention which explains the structure of the present invention, diagrams of the embodiments of the invention are employed in order to facilitate understanding of the present invention; however, the present invention is not limited to these embodiments of the invention.